1. Field of the Invention
This invention relates to an elastic composite with a substrate of consolidated entangled web.
2. Description of the Related Art
A conventional elastic nonwoven composite can be made by combining an elastomeric sheet with a necked nonwoven fabric, as described in U.S. Pat. No. 4,981,747, U.S. Pat. No. 5,114,781, U.S. Pat. No. 5,116,662, U.S. Pat. No. 5,226,992, U.S. Pat. No. 5,883,028, U.S. Pat. No. 5,910,224, U.S. Pat. No. 6,465,073, and U.S. Pat. No. 6,914,018. However, such an elastic composite using a necked carded, spunbond, or meltblown web as a substrate and wherein the tensile strength and tearing strength of such a web is dependent on its thermal bonding is typically unsuitable for many commercial applications due to inferior tearing strength in the machine direction.
U.S. Pat. No. 4,965,122 discloses a sequential thermo-mechanical method of necking the width of a thermally bonded nonwoven web by slowly stretching the web at ambient temperature before subjecting it to a heat setting process. The fiber binding and tensile strength of the resultant web is significantly reduced by this room temperature stretching and some webs can even be broken at draw rates as low as 10%. U.S. Pat. No. 5,492,753 describes an opposite sequential method for treating easy-to-break webs of meltblown fibers by slowly heating the precursor before transferring to a stretching step at ambient temperature. U.S. Pat. No. 5,244,482 and EP 1538250 A1 have shown that thermally bonded nonwoven fabrics can be necked-down to a certain width by simultaneously applying heat and stretch. While applying a uniaxial draw to a web and heating the web at an elevated temperature that is between the softening point of thermoplastic fibers and melting point, the majority of the fibers aligns in the direction of the draw and thereby become a necked fabric with a resultant width reduction.
The consolidation methods described in the prior art actually require precursor webs to contain non-elastomeric thermoplastic fibers and to have been subjected to thermal-mechanical bonding or calendering. The precursor of such a necked nonwoven web can be selected from a carded, spunbond, or meltblown web wherein the tensile strength and tearing strength of such a web is dependent on its thermal bonding. Because only a minority of fibers remain that are oriented crosswise to the direction of drawing after the consolidation process, there is a significant loss in tearing strength in the resultant necked fabric in the draw direction.
An entangled fabric with high tearing strength would be desirable. However, conventional spunlaced and needle-punched fabrics do not lend themselves to the heat-stretch elastication process as described in the prior art because the “bond points” are formed by entanglement, which provides only frictional and interlocking contact points that are not permanently altered by such a process.